Dosing devices for liquid chromatographs are known which comprise an actually movable shank being guided in packing sleeves and having a notch capable of receiving a sample and transferring it between a sample chamber and a high pressure chamber through at least one packing sleeve. The high pressure chamber is typically connected to the chromatograph flow system between the pump and the column. Such dosing devices have the disadvantage that the notch must be moved through the packing sleeve which forms a seal between the two chambers. Since this seal must withstand high pressures, the packing sleeve must be strongly pressed against the shank. This causes a certain deformation of the packing sleeve. Thus, it penetrates into the notch when the notch is passing the packing sleeve, even if the notch has rounded edges. The resulting substantial friction effect leads to abrasion of the packing sleeve particles. Consequently, the sample becomes contaminated, and the seal is demolished after a relatively short operation time.